Wave
Power

Waves
are a result of the effects of wind on the oceans and seas. This wind originates
from the major influx of energy to this planet: solar energy from the sun. The
energy contained within waves is around the world is huge; in some places values
of 70MW/km of wave front are experienced. In theory it could then be said that
huge generating stations could be built which would capture all this energy
and supply all or most of our needs. But there are many factors affecting this
kind of deployment becoming a reality.

Waves
are not as consistent as the tide and therefore there is a definite problem
with matching supply and demand. This is one of the main reasons that Wave power
has so far been restricted to small scale schemes, no large scale commercial
plant is in action.

Identifying
areas of suitable wave height is something that has to be done before deployment
can start. The highest concentration of wind power is found in the windiest
areas, which are mainly between latitudes 40 and 60 in both northern and southern
hemispheres. We are lucky in the Scotland to have an abundance of Wave Energy
available, mainly on the west coast. The following diagram shows the variation
in wave height around Britain during the Christmas Eve, 50 year storm of 1999.
The technology must be able to withstand the freak wave heights that can be
experienced, in rough and remote locations where access can be difficult.

There
are three main categories that wave power can be split into, these are Near
Shore, At Shore and Off Shore. There are obvious environmental and social
considerations to go with both of these conditions.

Near
Shore operations have to consider the aesthetic influence they will have on
what could be a picturesque area, they also will have a definite impact on shipping
and marine life but again this will be no greater than current offshore installations.
It has been suggested that a distance of 12 miles from shore is the distance
within which a device is said to be near shore.

The
issues discussed previously will also obviously be experienced by off shore
wave installations. It has been suggested that a depth greater than 50m will
constitute an offshore device.

On
shore wave power will have a marked effect on the area it is deployed. There
are ways of incorporating it into existing structures to minimise the effect,
such as harbour walls.

This
type of device floats on the surface of the water or below it. It is moored
to the seabed by either a taught or loose mooring system. One example of this
type of device will be discussed, the Edinburgh or Salter Duck. The Duck team
is led by Professor Salter at Edinburgh University.

The
Duck is shown in the figure below. Ducks work by independently rotating about
a long linkage; this maintains its stability by out spanning wave crests. The
front edge of the duck matches the wave particle motion. In moderate seas, the
more cylindrical back portion creates no stern waves but when the weather is
bad these parts shed energy through wave making to the rear. The device requires
a depth of at least 80 metres and uses a system of weights and floats to give
almost constant tension in the mooring cables.

This
type of device follows the motion of the waves; it creates power using the motion
at the joints. It is commonly moored slackly to hold it in place. One example
of this type of device is the Pelamis WEC that is being developed by Ocean Power
Delivery.

As
the Pelamis moves with the waves, the motion is resisted at the joints by hydraulic
rams that pump high-pressure oil through hydraulic motors via smoothing accumulators.
These motors are used to drive generators to create power. It has been said
that a 750kW device would be 150m long and 3.5m in diameter and comprise five
sections.

This
method of generating power from the tide works by using a column of water as
a piston to pump air and drive a turbine to generate power. This type of device
can be fixed to the seabed or installed on shore.

In
Scotland, the Government awarded three wave energy projects under the Scottish
Renewables Obligation. Only one of these projects has been realised and is generating
power in Scotland as this pack is being written, this is the LIMPET 500 on the
Island of Islay of the west coast, enabling the Island to take a step towards
becoming self sufficient in renewable energy. For more information see the LIMPET
Case Study.

At
present, the main stumbling block to deployment of wave energy devices is funding.
The Government has a very important role to play if this industry is to be given
the chance to fulfil its potential. The capital costs are the problem, as it
is hard to get companies to invest in technologies that have not yet been completely
proved. Similar to other forms of renewable energy sources such as wind and
solar, the fuel is free for the complete lifetime of the scheme.

Wave
devices that are on-shore have social implications for the surrounding area.
They can be integrated within harbour walls, which can affect shipping and cause
noise pollution. They can create employment in the area and attract visitors.

Offshore
devices have an effect on navigation and consultation with affected bodies must
be undertaken. The experiences of other offshore industries, such as oil, should
aid this part of planning for wave devices.

There
can be environmental impacts resulting from wave powered devices. But, like
other renewables, these impacts must be compared to the effects of fossil or
nuclear generation.

Devices
that are on-shore can have environmental benefits, such as helping to reduce
the erosion of the landscape. Any devices off shore can have an effect on the
aquatic life in that area but this again is very site specific and hard to predict.
But anchoring systems can become almost like artificial reefs, creating a place
for new colonisation.

Wave
power has a potential to play an important part in the long-term goal of utilising
renewable energy in Scotland. The deployment of the LIMPET 500 has brought recognition
to the technology available in Scotland. This interest will stimulate the growth
of the industry allowing other technologies to advance and realise their potential.
Until they become economically viable and more competitive with other renewables
such as wind, it is more likely that wave powered generation will supply islands
or small communities within Scotland.